1. Field of the Invention
The present invention is broadly concerned with desulfurization of liquid hydrocarbons such as crude oil, fuels and derivatives thereof. More particularly, the invention is concerned with compositions which can be directly contacted with liquid hydrocarbons to effect substantial desulfurization thereof, as well as methods of preparing and using the compositions. The compositions of the invention preferably are made up of solid or liquid blends including therein an alkylphenol ethoxylate, an amine, and a nitrite.
2. Description of the Prior Art
The concentration of sulfur in crude oil is typically between 0.05 and 5.0% (by weight), although values as high as 13.95% have been reported. In general, the distribution of sulfur in crude oil is such that the proportion of sulfur increases along with the boiling point of the distillate fraction. As a result, the higher the boiling range of the fuel the higher the sulfur content will tend to be. For example, a middle-distillate-range fraction, e.g., diesel fuel, will typically have a higher sulfur content than the lower-boiling-range gasoline fraction. Upon combustion, the sulfur in fuels can contribute to air pollution in the form of particulate material and acidic gases, such as sulfur dioxide. To reduce sulfur-related air pollution, the level of sulfur in fuels is regulated, and to meet these regulations sulfur must be removed from fuels during the refining process.
Refineries remove organic sulfur from crude oil-derived fuels by hydrodesulfurization (HDS). HDS is a catalytic process that converts organic sulfur to hydrogen sulfide gas by reacting crude oil fractions with hydrogen at pressures between 150 and 3,000 lb/in2 and temperatures between 290 and 455° C., depending upon the feed and level of desulfurization required. Organic sulfur compounds in the lower-boiling fractions of petroleum, e.g., the gasoline range, are mainly thiols, sulfides and thiophenes, which are readily removed by HDS. However, middle-distillate fractions, e.g., the diesel and fuel oil range, contain significant amounts of benzothiophenes and dibenzothiophenes (DBTs), which are considerably more difficult to remove by HDS. Among the most refractory of these compounds are DBTs with substitutions adjacent to the sulfur moiety. Compounds of this type are referred to as sterically hindered compounds because the substitutions are believed to sterically hinder access of the sulfur atom to the catalyst surface. Due to their resistance to HDS, sterically hindered compounds represent a significant barrier to reaching very low sulfur levels in middle- and heavy-distillate-range fuels. The high cost and inherent chemical limitations associated with HDS make alternatives to this technology of interest to the petroleum industry. Moreover, current trends toward stricter regulations on the content of sulfur in fuels provide incentive for the continued search for improved desulfurization processes.
Biodesulfurization has been studied as an alternative to HDS for the removal of organic sulfur from fuels. The use of hydrocarbon degradation pathways that attached DBT were unsuccessful because these systems relied on the oxidation and mineralization of the carbon skeleton instead of on sulfur removal and therefore significantly reduced the fuel value of the desulfurized end product. More recently, bacteria that desulfurize DBT and a variety of other organic sulfur compounds typically found in petroleum oils via a sulfur selective oxidative pathway that does not remove carbon have been isolated. This pathway involves the sequential oxidation of the sulfur moiety followed by cleavage of the carbon sulfur bonds.
Despite all of these well-known desulfurization efforts, there still exists a need for easy and cost-effective desulfurization of liquid hydrocarbons, using readily available components and a simplified removal mechanism.